Dental material

ABSTRACT

A white, substantially non-iron containing dental material formed from Portland cement. The material may be a dental cement, dental restorative or the like.

RELATED APPLICATIONS

[0001] This is a continuation application of pending U.S. patentapplication Ser. No. 10/038,786 (Case TUL-LOMA) filed on Jan. 3, 2002;which claims priority of U.S. provisional patent application Ser. No.60/259,685 (Case TUL-LOMA) filed on Jan. 4, 2001.

TECHNICAL FIELD

[0002] The present invention is directed toward a dental material, suchas a cement or a restorative material. More particularly, the inventionrelates to a dental material that is prepared with a Portland cement.Specifically, the invention is such a material that is substantiallyfree from iron oxide, and which has a CaO content of from about 50 toabout 75 percent by weight and an SiO₂ content of from about 15 to about25 percent by weight.

BACKGROUND OF THE INVENTION

[0003] U.S. Pat. No. 5,415,547 describes a composition of cement fordental applications. However, the composition of that Portland cement isgray in color. This color is deleterious in dental applications. Thegrayness of the cement produces a very un-esthetic result when thecement is visible through thin tissue, such as in the smaller teeth inpedodontics, or at the gum line. According to the present invention, twotypes of white cement can be substituted for such a gray Portlandcement: white Portland cement or calcium aluminate cement. A whitecement has an advantage of being more similar in tooth color to teeththan the '547 patent. Therefore, the dark color from a conventional,gray Portland cement will not be present.

SUMMARY OF THE INVENTION

[0004] It is an object of the invention to provide a dental material.

[0005] It is another object of the invention to provide a white dentalmaterial, such as a cement, a restorative or the like.

[0006] It is an additional object of the invention to provide such adental material that contains Portland cement.

[0007] It is a still further object of the invention to provide such amaterial that is substantially free of iron oxide.

[0008] A white Portland cement according to the invention containsvirtually no iron, unlike the '547 patent composition which containsabout 5% iron oxide. Without iron oxide, the cement will have a whitecolor, and fall within the compositional range of Portland cements,given as follows, all percents being by weight:

[0009] 61 to 70% calcia

[0010] 19 to 29% silica,

[0011] 5 to 15% alumina and

[0012] 0 to 0.5% iron.

[0013] Preferably the material contains less than about 0.5 percent byweight of iron, based upon 100 percent by weight of the material.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0014] A dental material such as a cement, restorative or the like,according to the invention, preferably has the following percentages byweight of components:

[0015] 61 to 70% calcia

[0016] 19 to 29% silica,

[0017] 5 to 15% alumina and

[0018] 0 to 0.5% iron.

[0019] Preferably the material contains less than about 0.5 percent byweight of iron, based upon 100 percent by weight of the material. Morepreferably, the material according to the invention is substantiallyfree of iron oxide, meaning that it contains less than about 0.5 percentby weight of iron. Most preferably, the inventive material contains noiron. The material is visually observed to be white in color, and istherefore, more desirable in dental applications than gray-coloredmaterials previously employed. A comparison of one embodiment of thepresent inventive material to known gray-colored materials is providedin TABLE I. TABLE I Normalized Composition of Cement Samples US ‘547Colton Exemplary Inventive Component Patent Fast Set White MaterialCalcia 65.00 64.2  68.9 Silica 21.00 20.8  25.2 Iron oxide 5.00 4.3 0.3Alumina 4.00 3.9 2.0 Magnesia 2.00 3.2 0.6 Sulfates 2.50 2.6 2.2 Soda,potassia <0.5 0.6 0.4 Titania — 0.2 0.07 Phosphorous pentoxide —  0.090.12 Manganese oxide —  0.05 0.02 Strontia —  0.07 0.13 LOI — 1.3 1.0 As(ppm) —  16** ND Pb (ppm) — 4.2** ND

[0020] Without iron oxide, the Portland cement has less of thecalcium-alumino ferrite phase, as noted in Table II. TABLE IIComposition by Phase of Cement Samples Exemplary Prior ExemplaryInventive Component Material White Material 3CaO.SiO₂ 62 68 2CaO.SiO₂ 1120 3CaO.Al₂O₃  3  5 4CaO.Al₂O₃.Fe₂O₃ 13  1 TOTAL Crystalline Phases 8994

[0021] White Portland cements are primarily used in decorativearchitectural applications, although their properties are similar tothat of gray cements. See Table III, where the “Exemplary Prior Cement”is manufactured according to the '547 patent, and is commerciallyavailable. The expense to exclude iron oxide from their formula makesthem more expensive and more difficult to manufacture. TABLE IIIPhysical Properties of Cement Samples Exemplary Exemplary PriorInventive White Property Cement Material Surface area (m²/kg) 451   409Particle Size distribution 90% finer than (μm) 27   25 50% finer than(μm) 9.4    9 10% finer than (μm) 1.85    3 Setting time, initial (min.)47   74 Setting time, final (min.) 332   210 Compressive strength (psi)after 1 day 1,550 2,370 after 3 days 3,900 4,120 after 7 days 5,3005,360 Sulfate, weight % of cement: as gypsum, CaSO₄.2H₂O 0.2 notdetected (K₂SO₄.CaSO₄.H2O) % plaster (hemi-hydrate) 86   50 (calculatedas % SO3)

[0022] Calcium aluminate cements can be used instead of a white Portlandcement. The calcium aluminate cements contain from about 32 to about 57weight percent alumina, and are clearly outside the '547 patentedcomposition. The silica content is usually less than 6 weight percent,the iron content is less than 20 weight percent (especially low whenwhite cement is needed), and the titania content is also less than 2percent. Titania makes the cement whiter.

[0023] The calcium aluminate cements generally set in one-half the timeof Portland cements. However, a very fast set may be achieved bycombining calcium aluminate and Portland cements. A “flash” setphenomena can occur where the setting time is reduced to less than 1hour when a 50/50 mixture of calcium aluminate and Portland cements ismade. TABLE IV shows that calcium aluminate cements set more quicklythan do Portland cements. In this graph, the final set time is about4.25 hours for a calcium aluminate cement, and about 7 hours for aPortland cement.

[0024] FIG. 1: Setting time of Portland and calcium aluminate mixtures.

[0025] Calcium aluminate cements can be stronger than Portland cements,in some cases twice as strong when fully set. Furthermore, calciumaluminate cement develops its strength sooner. Calcium aluminate cementsan achieve 50% of their total strength in less than 1 day whereas aportland cement may require between 1 and 6 days to achieve 50% of theirfinal strength.

[0026] Calcium aluminate cements are not usually used in applicationsthat hover around ambient temperature; they are usually used forrefractory applications. Below 27° C., an unstable hydrate is formed:CaO.Al₂O₃.10H₂O. Above 27° C. these hydrates release their water in aprocess called conversion and form the stable hydrates of2CaO.Al₂O₃.8H₂O, 3CaO.Al₂O₃.6H₂O and Al₂O₃.3H₂O. Unfortunately thisprocess creates pores that reduce the strength. We have a uniquesituation in dentistry with using calcium aluminate cements in the bodywhere the temperature is constant and above 27° C. Therefore, a stablehydrate can be formed that does not convert. High strengths and quicksetting scan be achieved without risk of conversion.

[0027] Sample compositions of two inventive calcium aluminate cementsare given in Table V, compared to a gray and two inventive whitePortland cements. TABLE V Comparison of Cement Compositions Type CementPortland Colton Portland Portland Calcium Calcium Oxide Fast Set WhiteWhite Aluminate Aluminate Calcia 64.2 66.3 68.2 29.8 33.9 Alumina 3.94.3 1.9 56.5 53.0 Silica 20.8 21.9 24.8 2.9 2.2 Iron oxide 4.3 0.3 0.41.3 1.1 Magnesia 3.2 2.0 0.5 0.4 0.7 Sulfate 2.5 3.3 2.2 0.2 0.0Potassia 0.3 0.3 0.1 0.1 0.2 Soda 0.3 0.1 0.1 4.8 4.7 Strontia 0.1 0.10.1 0.0 0.0 Manganese oxide 0.1 0.0 0.0 0.0 0.0 Phos. Pentoxide 0.1 0.10.1 0.1 0.0 Chlorine 0.0 0.0 0.1 0.0 Scandia 0.0 0.0 0.1 0.1 Titania 0.20.2 0.1 2.1 2.2 Bromine 0.0 0.0 0.1 0.2 Chromia 0.0 0.0 0.0 0.1 Zirconia0.0 0.0 0.1 0.0 Silver oxide 0.0 0.0 1.0 1.1 Platinum oxide 0.0 0.0 0.10.0 TOTAL 100.0 100.0 100.0 100.0 100.0

[0028] According to the invention, fluoride can also be added to aPortland cement in the form of calcium fluoride. Additions of 1.7 wt %fluorine in the cement before firing, increase the strength (at 28 daysof setting) about 10%. The fluoride may or may not be released from sucha cement.

[0029] Some dental applications do not require high radiopacity, such aspulp capping. The sealing and capacity for dentinal bridge formation aremore important than radiopacity for use of the material in a thin layerrequired for pulp capping. For added effectiveness in some dentalapplications, a cement can be made radiopaque. For instance, with theaddition of 20 wt % bismuth oxide, the mixture will have a radiopacityequal to 3 mm of aluminum at a cement thickness of 1 mm. The gray andwhite portland cements have equal radiopacity, 3 mm of Al equivalent, at1 mm of cement thickness, when blended with 20% bismuth oxide. As muchas 40% bismuth oxide can be added to the mixture, however, the bismuthoxide slows the setting and strength development. The bismuth oxideimparts a pale yellow color to the mixture because the bismuth oxide isyellow-colored.

[0030] Another radiopacifier can be blended with the cement. Forinstance, a radiopaque glass used for dental composites can be mixedwith portland cement, as an alternative to bismuth oxide. The color ofthe mixture is white. A glass such as Corning 7724 or 7726 can be used.Such glasses are covered under U.S. Pat. No. 4,920,082 or 4,775.646,respectively. If a fluoride-releasing glass is used, this mixture wouldbe radiopaque and release fluoride ions. The fluoride release would helpprevent internal resorption or cervical decay.

[0031] A third radiopaque addition would be barium sulfate instead ofbismuth oxide. The barium sulfate is not soluble in water; therefore itwould not be a toxic heavy metal compound. This material is white andwould also avoid gray coloration of the mixture.

[0032] Another addition to cement is Bioglass. Bioglass, a patentedformula of glass, is known to be biologically active, and encourage bonegrowth (see U.S. Pat. No. 4,232,972). Its formula is within thiscompositional range (all percentages Silica 40-62% Soda 10-32% Calcia10-32% Phosphorous pentoxide  0-12% Calcium fluoride  0-18% and Boronoxide  0-20%.

[0033] The Bioglass can be added as coarse powder, about 170 to 140-meshsize. The large, coarse form of the glass has been found to be moreconducive to bone growth than a finer size. Bioglass particles could beused as an “aggregate” in a portland cement and create a concrete.Bioglass (see U.S. Pat. No. 4,775,646) is a white powder, and would notcolor a mixture with white cement. This would be of most interest forfilling bony defects or root-end filling where bone re-growth isimportant. Hench has patented the mixture of Bioglass and cement. SeeU.S. Pat. No. 4,775,646 to L. Hench et. al for a fluoride-containingBioglass. U.S. Pat. No. 4,171,544 to L. Hench et. al for bonding to bonewith a high surface area porous, silica-rich surface. This teaches aboutportland cement for BONDING (not as the restorative for) dentalimplants, and cement mixed with a biologically active glass.

[0034] Other compositions of cement can be considered to create a whitecement, as long as they do not include iron oxide. For instance, bariumoxide can be partially or wholly substituted for calcium oxide. This isa new ingredient, not specified in the first Torabinejad patent (U.S.Pat. No. 5,415,547). This would create a cement that is inherentlyradiopaque and needs no further additions.

[0035] The fineness of the cement also affects its usefulness indentistry. For instance the Torabinejad patent refers to cements of Type3, a relatively fine cement having a surface area of 450 to 550 m²/kg.However, such cements are perceived as grainy or sandy by dentists,having lesser quality, and less packable into fine orifices. The surfacearea measurement gives a general indication of the fineness of thepowder, but does not adequately characterize the distribution of thepowder particles sizes.

[0036] Two approaches can be followed to improve the performance of suchdental materials: removal of coarse particles, or reduction in theaverage particle size. The removal of coarse particles can be achievedby sieving or air elutriation. The particle size reduction can beachieved by milling processes such as ball milling, air attrition, orattrition milling.

[0037] Finer cements are more suitable for either a root canal sealingmaterial or a root canal obturation material. The use of a cement with asurface areas of about 1,000 m²/kg allows it to be easily filled in aroot canal, including lateral canals. We tested such a cement for a rootcanal sealer and found it preferable to a cement have a lower surfacearea. Furthermore, the removal of particles coarser than 400 mesh (44μm) improved the handling of the gray cement used in the commerciallyavailable ProRoot MTA material. This process increased the measuredsurface area from 454 to 509 m²/kg.

[0038] Therefore, it is apparent that a dental material according to theinvention as described above, is useful in meeting the stated objectivesof the invention. It will be understood that amount of variouscomponents, can be varied and still fall within the scope of theinvention. Similarly, specific formulation components as provided aboveare merely exemplary and other components similar or otherwise are alsowithin the scope of the invention. The scope of the invention will bedetermined only by the claims.

What is claimed is:
 1. A dental material comprising Portland cement andwhich contains less than about 0.5 percent by weight of iron oxide basedupon 100 percent by weight of the material.
 2. A dental material as inclaim 1 which is white in color.
 3. A dental material as in claim 1,comprising from about 61 to about 70 weight percent calcia, from about19 to about 29 weight percent silica, from about 5 to about 15 weightpercent alumina and from 0 to about 0.5 weight iron, based upon 100weight percent of the material.